These four pages from my notebooks show the various levels of a typical watchtower: from its roof to its lowest storey.

The right hand diagram on the first page shows the roof of the tower, with its six ribs emerging from the keel beam. It is on the ends of this beam that two of the deadman chairs are located.

Note the trapdoor opening down into the uppermost storey. Note also the staples climbing up the rib in the lower left which gives access to a naphtha flare and to the heliograph platform.

The left hand diagram shows the upper storey which provides accomodation for the staff of ammonites who operate the heliograph.

It is these chambers that Carnelian, his father and the other Masters occupy each night on their journey to Osrakum.

The second page shows the two storeys which are the barracks of the tower garrison.

The third page shows the storey of the tower which is level with the leftway.

In the upper part of the diagram is a cistern. Corresponding to this, in the lower part of the diagram, is the ramp that leads down into the stables.

A portucullis seals the entry from the leftway. Standing before this entrance is a monolith the purpose of which is to make it impossible to use a battering ram against the portcullis.

To the right of the portcullis you might be able to make out the faint sketch of an aquar as seen from above. I put this in so as to be able to more easily imagine what it would be like leading an aquar into this space.

A small diagram on the right hand side of this page is an elevation showing how the portcullis and its counterweights work. It also shows measurements for the heights of some of the storeys.

The fourth page shows two of the three stable levels which are linked to the upper entrance by ramps. Various other mechanisms are lodged here which have to do with the operation of the portcullis etc in the levels above.

The lowest level of all is the uppermost diagram on the fourth page.

Note that it too has a portcullis and a monolith set facing it. This gives direct access to the road running along the foot of the leftway.